1. Field of the Invention
This invention relates to a magnetic transfer apparatus in which information carried by a master information carrier is magnetically transferred to a slave medium.
2. Description of the Related Art
This invention is applied to a magnetic transfer where a magnetization pattern representing information carried by a master information carrier (a patterned master) is transferred to a slave medium having a magnetic recording portion by applying a transfer magnetic field to the master information carrier and the slave medium in close contact with each other. The master information carrier (a patterned master) has a magnetic layer at least on the surface thereof and carries an embossed pattern (a pattern of protruding portions and recessed or not-protruded-portions) or an embedded structure representing a transferred pattern representing the information to be transferred to the slave medium such as a servo signal.
When the slave medium is a disk medium such as a hard disk or a high-density flexible disk, the master information carrier is held in close contact with one or each side of the slave medium and the transfer magnetic field is applied to the slave medium and the master information carrier(s) in this state by a magnetic field application means comprising an electromagnet or a permanent magnet disposed on one or each side of the slave medium/master information carrier assembly.
In order to transfer the information in a good quality, it is important to hold the slave medium and the master information carrier in uniform close contact with each other. That is, when there is defect in close contact between the slave medium and the master information carrier, there is generated an area where no magnetic transfer occurs, which results in a signal missing in the information transferred to the slave medium and deterioration in quality of the signal transferred. When the transferred information is a servo signal, the signal missing results in an unsatisfactory tracking and deteriorates the reliability of the slave medium.
In the magnetic transfer, placing the slave medium and the master information carrier in a holder comprising a pair of holder halves which can be moved toward each other to hold the slave medium and the master information carrier in close contact with each other is advantageous in holding the slave medium and the master information carrier in close contact with each other uniformly over the entire area. See, for instance, U.S. patent Laid-Open No. 2002/030909.
In the holder, the master information carrier and the slave medium are brought into close contact with each other and pressed against each other generally by fastening by the use of screws or by mechanical pressing by the use of a power source such as an air cylinder or an electric motor.
There has been proposed a magnetic transfer apparatus in which a slave medium is received in a recess formed on one side of a holder and a flexible master information carrier is placed on the recess to hermetically close the recess, and the inner space of the recess is evacuated so that the master information carrier is deformed to be brought into close contact with the slave medium under vacuum. See, for instance, Japanese Unexamined Patent Publication No. 2002-367161.
In the conventional magnetic transfer apparatus, the holder must be high in rigidity in order to push by a power source the master information carrier and/or the slave medium toward each other to press them against each other and to cause the pushing force to act over the entire area of the master information carrier and/or the slave medium. On the other hand, it is advantageous to dispose the magnet as close to the slave medium/master information carrier assembly as possible in order to apply the transfer magnetic field. This limits the thickness of the holder wall. Accordingly, the rigidity of the holder becomes insufficient to uniformly press the master information carrier and the slave medium against each other.
In the case where the power source acts on the central axis of the slave medium/master information carrier assembly, though the central portions of the slave medium and the master information carrier can be applied with a large pressure, the peripheral portions of the slave medium and the master information carrier are applied with a smaller pressure, and accordingly, it is difficult to apply a uniform pressure.
On the other hand, in a magnetic transfer apparatus in which a slave medium is received in a recess formed on one side of a holder and a flexible master information carrier is placed on the recess to hermetically close the recess, and the inner space of the recess is evacuated so that the master information carrier is deformed to be brought into close contact with the slave medium under vacuum as disclosed in Japanese Unexamined Patent Publication No. 2002-367161, very high precision is required in making the master information carrier and the portion of the holder on which the master information carrier is rested. Small fluctuation in the height of the portion of the holder on which the master information carrier is rested can result in defective close contact between the slave medium and the master information carrier. When the master information carrier is deformed each time the inner space of the recess is evacuated due to fluctuation in the height of the portion of the holder on which the master information carrier is rested, the service life of the master information carrier, which is expensive, can be shortened. Further, this mechanism is disadvantageous in that the master information carrier and the slave medium cannot be pressed against each other at a pressure higher than the atmospheric pressure.